The present invention relates to a sensor unit for determining properties of a lubricant, for example, of a lubricating grease in a rolling bearing. The invention also relates to a machine element with the sensor unit according to the invention and a machine assembly with the machine element according to the invention.
DE 10 2007 042 254 A1 shows a measurement device for analyzing the lubricant in a bearing. This measurement device comprises a transmitter for transmitting infrared radiation that is directed onto a test area and is reflected back from the specimen onto a receiver. The test area is arranged in the interior of the bearing. In particular, IR radiation in the area of combination methods of the C-H oscillations are detected and spectrally analyzed by the receiver. In this way, the lubricant can be continuously monitored during operation and an alarm can be output when the lubricant is to be changed. In the embodiment shown, the transmitter and the receiver are located with a unit for signal conditioning in a common housing. In this housing there are components for signal evaluation by which, for example, calculated properties of the lubricant can be output directly as a digital signal.
DE 10 2010 031 919 A1 teaches a measurement probe for a sensor for analyzing a medium by infrared spectroscopy. With this measurement probe, for example, the lubricant of a bearing can be analyzed. The measurement probe comprises an infrared transmitter and an infrared detector, as well as a reference detector. The infrared detector and the reference detector are arranged on surfaces arranged at a distance from each other. From the infrared transmitter, IR radiation is incident on the medium and is reflected back onto the infrared detector. Furthermore, IR radiation from the infrared transmitter is incident on a mirror surface and is reflected back onto the reference detector. The infrared transmitter and the reference detector are arranged on one carrier. The mirror surface and the infrared detector are formed on opposite sides of a bridge element, wherein the carrier and the bridge element are arranged at a distance from each other. This produces a three-dimensional setup for the components.
From DE 10 2009 037 424 A1, a bearing arrangement is known in which a lubricant sensor transmits information on the state of the bearing to a central receiving station via a transmitter.
DE 10 2010 015 084 A1 shows a sensor part for an infrared sensor for spaced-apart arrangement of an infrared transmitter, an infrared detector, a reference source, and a reference detector.
From the product information sheet “State monitoring of lubricating greases in roller bearings” published by Schaeffler Technologies GmbH and Co. K G, September 2010 and from the product information sheet “FAG GreaseCheck” published by Schaeffler Technologies AG and Co. KG, August 2013, a lubricating grease sensor is known that is provided, in particular, for monitoring the lubricating grease in roller bearings. The lubricating grease sensor comprises a cylindrical sensor head that projects directly into the roller bearing. The sensor head is connected by a cable to evaluation electronics that are arranged in a larger housing at a distance to the sensor head. Analog signals are transmitted from the sensor head to the evaluation electronics. Therefore, the length of the cable must not be greater than one meter. The evaluation electronics in the additional housing makes the use of the lubricating grease sensor more difficult.